Poppet valves are widely used for opening and closing flow paths for gases and liquids, for example, as shift diverter valves in vehicles; for channeling hydrogen into reformers in fuel cells; and as intake, exhaust, and exhaust gas recirculation valves in internal combustion engines. A poppet valve comprises a typically circular valve head mounted transversely on a pintle shaft for axial motion thereof to form or eliminate a flow gap between the valve head and a mating circular valve seat in a valve base. A pintle shaft is also known as a valve shaft or valve stem.
Poppet valves can be very demanding in their design and fabrication tolerances. For example, some poppet valves are provided with conical mating surfaces on the valve head and valve seat; however, leak-free sealing over the entire mating surfaces depends on near-perfect circularity and smoothness of both surfaces. In addition, the surfaces must have substantially identical cone angles. The highest quality valves are ground on a precision lathe and then the valve head is lap-ground to its dedicated seat. This is labor-intensive, time-consuming, and expensive. U.S. Pat. No. 4,565,217 discloses a poppet valve having a conical head and a curved seat such that the head and seat can seal along a circular line of contact, thereby obviating the need for matching cone angles.
A further requirement for leak-free sealing is concentricity of the head and valve. Typically, concentricity is provided by the precision placement of a valve shaft guide on the co-axis of the valve head and valve seat, as disclosed, for example, in U.S. Pat. Nos. 4,565,217 and 4,907,741. Control of concentricity may be further enhanced by providing a second shaft guide opposite the first, such that the valve head is guided on both sides; see, for example, U.S. Pat. Nos. 4,915,134; 5,211,198; 5,899,232; and Re.33,246. Such precision guiding of a poppet valve shaft can be costly and cumbersome to provide, and expensive to maintain, particularly in poppet valves wherein the diameters of the valve and seat are large relative to the diameter of the shaft or stem.
A problem with shaft guides generally is that clearance between the guide and the shaft represents a potential source of leakage from the valve. U.S. Pat. No. 5,467,962, the disclosure of which is incorporated herein by reference ('962), discloses an actuator housing having a linear bearing (valve guide) which is operable both to align the valve stem within the valve base and to define a seal between the base and the housing. The clearance required between the solenoid armature and the armature shell prevents precise alignment thereby of the valve stem in the valve body. Therefore, a small radial clearance is provided between the bearing and the actuator housing, preferably about 0.2 mm, which allows some limited side-to-side or radial movement of the valve and stem, permitting compliant centering of the valve stem and head by contact with the valve seat. This also permits an extremely close tolerance between the valve stem and the bearing, enhancing shaft sealing thereby. A face seal between the bearing member and the actuator housing prevents leakage around the bearing member. Thus, sealing between the bearing and the housing is maintained regardless of radial movement of the bearing in the housing or the position of the valve stem within the bearing. A shortcoming of the disclosed apparatus is that a single coil spring, disposed on axis between the bearing and the solenoid armature, functions both to bias the face seal and to return the armature upon deactivation of the solenoid. The spring must be sufficiently strong to ensure the bearing face seal, but the stronger the spring, the greater the force the solenoid must overcome in closing the valve. In general, a single spring cannot be optimized for both functions.
Further, known poppet valves require that the valve head be mounted perfectly orthogonal to the valve stem and that a plane containing the valve seat be perfectly parallel to a plane containing the valve head. Any significant deviation in any one of these relationships can cause the head to mate imperfectly with the seat, which can result in valve leakage.